Each dot is calculated carefully by a python script and each portrait takes a day to calculate. Unlike classical art where shapes are made of millions of brush strokes or chisel marks that can tolerate "mistakes" this can not. It's more like iconography, every dot matters, even a millimetre deviation will cause a blurry result or distorted face.
Once the calculation is done, I transfer dots into wood and hammer nails with the same precision. It took me a long time to develop muscle memory to reach the level of precision needed. Every nail is placed within a quarter of a millimetre precision, exactly 90 degrees to the board and same height.